Mycoplasma, belonging to the class Mollicutes, is a bacterium that does not have cell wall. Mycoplasma has a size of about 0.2 to 0.8 μm and can pass through a 0.2 μm filter. Typically, mycoplasma contaminates cells during cell culturing, and in particular, mycoplasma, such as Mycoplasma hyorhinis, Mycoplasma fermentans, Mycoplasma orale, Mycoplasma argininii, Mycoplasma hominis, or Acholeplasma laidlawi, contaminates cells during cell culturing in pharmaceutical companies, hospitals, and college laboratories where cell culturing is frequently conducted. In general, mycoplasma contaminations occur during cell line construction from a living organism infected with mycoplasma, and furthermore, serum and carelessness in laboratories bring about contaminations between cell lines, thereby resulting in mycoplasma contamination all over the laboratories.
Reportedly, in the USA, about 15% of cell lines are contaminated with one or more species of mycoplasma. Such a large proportion may be due to the fact that mycoplasma is not accompanied with visible changes, such as an increase in a turbidity of a medium as in the case of other infection sources (i.e., bacteria having cell wall or fungi), or cell death as in the case of virus. Thus, experimenters fail to recognize the contamination and spread the contamination. Also, due to the absence of cell wall, mycoplasma is not affected by penicillin and other beta lactam antibiotics which are typically used in culturing cells.
Although mycoplasma contamination is not accompanied with visible changes in culturing cells, it causes various unpredictable outcomes. One of the most representative unpredictable outcomes is induction of abnormal cytokine expression in cell lines by changing the metabolism of infected cell line. Therefore, many experiments and studies produce abnormal results stemming from the mycoplasma contamination. Also, mycoplasma may change the shape of cells, and may consume a metabolite required to synthesize DNA or RNA, thereby affecting a metabolism of nucleic acids. Therefore, conformation of receptors or membrane proteins on cell membrane are changed, and thus, cellular immunity or a signal transmission system are disturbed and cell growing rates are changed, thereby causing unpredictable results for example in cell-growth studies or cytotoxicity studies. Also, mycoplasma contamination changes nucleic acid metabolism and/or metabolism of infected cell line, and thus, virus production using the infected cell line is also reduced. In particular, when a monoclonal antibody is produced, the fusion rate of hybridoma cells may be decreased, and also, antibody production is substantially decreased, leading to failures of experiments. Such phenomena may negatively affect production of biological preparations, for example, a vaccine. This shows that mycoplasma contamination causes serious problems even in respect to economy.
Despite such problems stemming from serious mycoplasma contamination accompanied with cell culturing, a method for removing the mycoplasma contamination to a satisfactory level has not been developed. Typically, the mycoplasma contamination is removed by using tetracycline or quinolone antibiotics, or by using non-antibiotics such as peptide and lipopeptide. In these cases, however, the mycoplasma contamination is not completely removed, and also, when these materials are used at a high concentration for complete removal, cytotoxicity or antibiotic resistance may occur.